Sensorium: the original raison d'etre of the motile cilium?

The role of non-motile (primary) cilia as sensory antennae critical for metazoan development and physiology has surfaced over the last decade, long after the function of motile cilia in propelling cells or moving fluids across tissues was well established. A new study of motile cilia from respiratory airways raises the possibility that transducing sensory cues from the environment is a universal characteristic of cilia and may have been the original raison d'être of the ancestral cilium.